The effects of moderate-intensity light (150-200 foot-candles) on the retina of vitamin A deficient (retinol deficient) and vitamin A adequate rats (retinol adequate) were examined. The structure of photoreceptor outer segments remained intact for a longer period of time in retinas of rats deficient in retinol (low levels of rhodopsin) after exposure to light. In addition, more photoreceptor cell nuclei remained after six days of exposure in the retinol deficient rats. These data are consistent with the hypothesis that rhodopsin is involved in initiating the process leading to the structural deterioration of retinal photoreceptors.